2. Field
This invention relates to control valves for dental syringes and the like. It is particularly related to valves suitable for the control of air or water through a dental syringe and operable, through a valve actuator, with the same hand with which the syringe is held by a user during dental operations.
2. State of the Art
As is shown in U.S. Pat. No. 4,026,025, it is known to position pushbutton-type actuators on the top of the head of a dental syringe. So positioned, the actuators can be conveniently manipulated to operate control valves internal the syringe. These valves in turn regulate the flow of air and water through the syringe head, and eventually to and through a syringe tip.
The '025 patent discloses a syringe head and tip unit that is typical of other known structures. In general, such units include a syringe head with air and/or water conduit connector(s). Air and/or water are each supplied under pressure through individual connectors to respective passageways in the head. A flow control valve is mounted in each such passageway. A separate passageway and flow control valve is provided for each connector. Thus, if a single air or water connector is provided, a single passageway and a single flow control valve will be present. Alternatively, if both air and water connectors are provided, separate valves will be present within each of two respective passageways.
The control valve provided for each passageway used is generally biased to its closed condition. It has been found that the valve unit commonly used in pneumatic tire stems (i.e., a Schrader valve), is a very suitable control valve for dental syringes. A typical dental syringe structure includes a Schrader valve threaded into the passageway between a connector and its associated outlet to the syringe tip.
A valve actuator is also mounted within and projects from the passageway. It is thus positioned for operation by a user selectively and intermittently to open the control valve. An open valve allows the flow of a utility from the connector to the tip.
U.S. Pat. No. 4,026,025 discloses a valve actuator which comprises a monolithic button with an O-ring fitted in a slot encircling the button. The button is inserted into the passageway, and friction between the O-ring and the passageway wall is relied upon to hold the button in place. One end of the button projects from the passageway, and is curved to accommodate finger feel of the user, while the opposite end is provided with a depression configured to receive an end of the actuator stem of the control valve. In use, the button and O-ring reciprocate together in the passageway, and the O-ring seals the unit to prevent flow past the button.
The valve actuator of the '025 patent is generally depressed by pressure applied to the top curved end by a user's thumb. When the pressure is released, the control valve is closed by a valve spring. The valve spring must also function to push the button further out of the passageway as the valve closes. Because only the frictional engagement between the O-ring and the passageway wall holds the button in the passageway, it is possible for the button to escape from its installed position. It may be inadvertently dislodged and pulled from the syringe head or it may fall from the head. Such an occurrence is especially likely after the button has been repeatedly removed and reinserted into the head. Under those circumstances, the O-ring tends to become worn.